The present invention relates to a method of injecting fuel into a combustion chamber of an air compressing, spontaneous ignition, internal combustion engine, with an adjustment member of a fuel injection nozzle or injector being actuated electrically and being controlled via an electronic circuitry, with the fuel quantity being withdrawn from a pressure chamber. The present invention also relates to various apparatus for carrying out such a method.
Increasingly stricter legislation with regard to the permissible levels of polluting emissions (hydrocarbons, nitrogen oxides), and also with respect to black smoke that is discharged, cause the developers of Diesel engines to strive to influence and control the course of combustion within an engine in such a way as to fulfill the aforementioned requirements.
The requirements for an ideal injection system are many, including, for example: performance range control of quantity, duration, and chronological beginning of "preliminary injection" and "main injection", which is ultimately a basis of an appropriate control of the fuel pressure in the injector chamber that determines the quality of the vaporization. With respect to a more uniform fuel distribution in the combustion chamber, it should furthermore be possible to be able to influence not only the mean drop magnitude (of the vaporized fuel), as well as the angle of the conical envelope, which includes the axial injection stream expansion, and t o do so intentionally within certain limits during an injection process It would also be advantageous to be able to additionally influence the penetration depth of the stream of drops into the combustion chamber.
Approaches that cover a portion of the aforementioned requirements have in the meantime become available via so-called pump-injector systems. The high injection pressure that can be realized therewith, accompanied by the resulting improved degree of vaporization of the fuel, explains, due to the better mixture preparation that is achieved, primarily the significant reduction in black smoke. Versions of the pump-injector system that are provided with by-pass pistons as means to realize a preliminary injection finally permit a shortening of the inition lag, resulting in a reduction in combustion noise. The realized performance range control of ignition start and ignition duration via electromagnetically controlled bypass valves (parallel to the injector) represents a high degree of flexibility with regard to influencing the course of combustion. The objective of ensuring for each load and speed point of the engine also always an optimum fuel introduction cannot always be fulfilled by the pump-injector concept. One of the problems is the dependency, which is known and encountered with conventional injection pumps, of the speed with which the injection quantity and pressure can be provided upon the momentary engine speed (displacement speed of the plunger). In order, for example to realize high injection quantities (per stroke) in respectively short time intervals at a low engine speed, another technique was required.
DE-OS 28 54 921 discloses an injector that is provided with electromagnetic actuation of the injector needle valve. A solenoid that actuates the injector needle valve can be excited by an electronic control mechanism. With such a feature the movement of the injector needle valve and hence the injection process, can be preprogrammed. However, the chronological movement progress of the injector needle valve is considerably limited by the inertia thereof, so that the possibilities for an electronic control can be utilized only to a limited extent precisely due to this inertia of the injector needle valve.
It is therefore an object of the present invention to induce the injected quantity of fuel as a function of time in order, for a more homogeneous mixture preparation, to be able to freely control the parameters of penetration depth and cone angle of the injection stream as well as the drop magnitude spectrum.